"Jonathan Morton" <chr### [at] chromatixdemoncouk> wrote in message
news:3D3### [at] chromatixdemoncouk...

> Hmmm...  First recall that POV-Ray, like all other tracers, shoots rays
> from the camera, not from the light sources.  When these rays hit an
> object, it then shoots rays *towards* each light source to see if it's
> in shadow or not.
>
> These shadow rays don't care whether the object they intersect happens
> to be part of a light-group or not.  They only care if the object the
> camera-ray hit was in the correct light-group.

Yes. Although I suppose it was a design choice, not a technical constraint
for the developers.

> Remember, a shadow is just an absence of light.  The shadow falls across
> a different object than the one you put in the light-group.  It is this
> shadowed object that needs to have the correct lights attached to it.



I think I understand the principle, but I still do not understand what you
meant about "complementary light-groups or something". If light_group has an
effect when deciding if an object is lit by a light_source but not when
deciding if an object is blocking a light_source (whether this object is lit
or not by that light is unimportant), I do not see how to get the effect I'd
like (a visible, shadow-casting light-source) with light_groups alone.





Philippe

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